1. Field of the Invention
The present invention relates to an access device for supporting a variable data layer, and in particular, to an improved access device for supporting a variable data layer which can minimize variations of system hardware constitution due to access variations of a physical layer unit.
2. Discussion of the Related Art
FIG. 1 is a block diagram illustrating a conventional access device for supporting 10 Base-T access of a physical layer. Referring to FIG. 1, the access device for supporting the 10 Base-T access includes a user access processing module unit 12 having an analog access processing unit 10 and a digital access processing unit 11; a central control processing module unit 16 having a time division multiplexing (TDM) switching unit 13, a voice processing unit 14 and a processor module unit 15; and a local area network (LAN) access processing module unit 18 having a LAN access processing unit 17. In the conventional access device, when the user inputs a command, the user access processing module unit 12 processes the command of the user and transmits the processing result to the central control processing module unit 16. The central control processing module unit 16 converts the command of the user into data usable in an external layer. The LAN access processing module unit 18 externally transmits the converted data from the central control processing module unit 16.
The operation of the conventional access device will now be explained. When the user inputs a specific command, if the inputted command is an analog data, such as a telephone or fax, the user access processing module unit 12 enables the analog access processing unit 10 to process the data. If a private exchange externally transmitting/receiving a digital data is engaged, the user access processing module unit 12 enables the digital access processing unit 11 to process the data. The data processed in the analog access processing unit 10 is transmitted to the TDM switching unit 13 through TDM bus A. The data processed in the digital access processing unit 11 is transmitted to the TDM switching unit 13 through TDM bus B.
The TDM switching unit 13 performs a switching operation between TDM buses A and B, and transmits the processed data to the voice processing unit 14 through TDM bus C. The voice processing unit 14 compresses the received voice data according to a compression method provided by a CPU 24 of the processor module unit 15, and transmits the compressed voice data to the CPU 24 of the processor module unit 15 through a host processor interface (HPI). The HPI bus acts as address/data buses for transmitting/receiving data to/from a processor of the processor module unit 15 and an auxiliary processor of the voice processing unit 14, and related control signals.
In order to transmit the compressed voice data to a corresponding system through the LAN access processing unit 17, the CPU 24 of the processor module unit 15 converts voice compression information and destination information into internet protocol (IP) frames, and transmits the frames to the LAN access processing unit 17. The LAN access processing unit 17 transmits the IP packet from the processor module unit 15 to an external IP network, such as the Internet.
When the packet is received from the external IP network, the LAN access processing unit 17 receives the IP packet and transmits it to the CPU 24 of the processor module unit 15. The processor module unit 15 extracts the IP frame from the IP packet, and extracts compressed voice data, voice compression information and destination information from the extracted IP frame. Then, the processor module unit 15 transmits the compressed voice data to the voice processing unit 14 through the HPI bus, transmits control information for restoring the voice compression data according to the extracted voice compression information, and transmits path control information of the TDM switching unit 13 according to the destination address.
The voice processing unit 14 restores the received voice data according to a restoring method provided by the CPU 24, and transmits the restored data to the TDM switching unit 13 through TDM bus C. The TDM switching unit 13 transmits the restored voice data from the voice processing unit 14 to the analog/digital access processing unit 10 or 11 of the user access processing module unit 12 through TDM bus A or B, maintaining the switching path transmitted from the CPU 24.
The aforementioned process will now be described in short in view of software processing. The access device receives a reset signal from a peripheral interface logic in the processor module unit 15 after receiving power, determines an operation state of the CPU, forms an initial setup for the operation of the CPU from a boot ROM memory, and downloads a program programmed by software operation from an application RAM region. The respective access processing units 10 or 11 of the user access processing module unit are initialized for operation. In addition, a switching path is set up for the TDM switching unit 13. A voice processing method selected with the corresponding system through the LAN access processing unit is designated in the voice processing unit 14, so that the voice processing unit 14 can compress the voice data received through the TDM buses and restore the compressed voice data received through the HPI bus.
As described above, the processor module unit 15 sets up the basic environment where the system can be operated as the access device. After the initial setup process, the CPU of the processor module unit 15 periodically tests and processes the respective processing units, transmits the voice compression data received through the HPI interface to the LAN access unit in the form of an IP packet, decomposes the IP packet received through the LAN access unit to extract the compression voice data, and transmits the extracted data to the voice processing unit through the HPI bus. The voice processing unit restores the compressed voice data.
The general access device supports a specific data layer of a specific physical layer. In order to support access of another or a different physical layer, the access device requires a special external system. For example, the access device for supporting the 10 Base-T which is a transmission path standard of the LAN where the physical layer is standardized as IEEE 802.3 cannot directly access an x-type digital subscriber line (xDSL) network.
FIG. 2 shows a structure for accessing the xDSL network by using the conventional access device for supporting the 10 Base-T. As illustrated in FIG. 2, the conventional access device for supporting the 10 Base-T cannot access the xDSL network. In order to access the xDSL network, the access device should use an xDSL modem, or remove the 10-Base T, receive a service function of an access device and use the access device accessing the xDSL.
As described above, the conventional access device accesses in an IP environment and supports a specific physical layer access unit. However, according to technical developments of the xDSL, the conventional access device requires a special external system or a new system to access the xDSL network. In addition, applicability of the hardware is reduced.